The acrylic rubber-metal composite prepared from a metal and an acrylic rubber by vulcanization bonding can be used in the production of parts requiring an oil resistance, a heat resistance, etc. Recently, a water resistance has been required in addition to the afore-mentioned characteristics in view of possible contamination of oil with water, depending on contacting service positions.
To improve chemical and physical bonding forces in the vulcanization bonding between the metal and acrylic rubber, a method for coating a zinc phosphate treated metal with a phenol resin-based adhesive is generally used. However, the zinc phosphate-based treating agent generally has a high crystallinity and the surface roughness of the metal treated with such an agent is so high as to cause a abrasion of mating materials when brought into contact with rubber-unbaked parts as a problem.
When a metal and an acrylic rubber are bonded to each other through only one layer of the adhesive without any surface treatment, on the other hand, a peeling problem occurs at the boundary surface between the metal and the adhesive in some tests of contamination of oil with water. To obtain the water resistance, it has been proposed to bond a metal to a rubber, using an undercoating adhesive and an overcoating adhesive, where the application of two layers of the adhesive has not any performance-wise problem, but a low productivity problem, because two units of adhesive applicators must be used.
Patent Document 1: JP-A-10-121020
Patent Document 2: JP-A-11-001672
Patent Document 3: JP-A-2000-017247